Headbox and method of regulating a headbox

Abstract: The invention concerns a method in the regulation of the headbox of a paper machine/board machine. In the method, an additional flow (Q 3.1 ,Q 3.2 ...Q 3.n ) is introduced into the pulp suspension at different points across the width of the headbox, the concentration of said additional flow (Q 3.1 ,Q 3.2 ...Q 3.n ) being regulated. The concentration of the additional flow is regulated by means of a mixer unit (22), which comprises a displaceable distributor part (26), whereby, when the mixing ratio is being regulated, the flow resistances of the component flows (Q₁,Q₂) entering into the mixer unit (22) are adjusted by displacing the distributor part (26,260) of the mixer unit (22) in the chamber (F) of the mixer unit (22).

Description: The invention concerns a headbox and a method of regulating a headbox of a paper/board machine, by means of which method and headbox it is possible to act upon the grammage profile of the paper reliably across the width of the paper web and favourably also upon the fibre orientation profile in the paper web across the width of the paper web. As is known from the prior art, the discharge flow of the pulp suspension out of the headbox must be of uniform velocity in the transverse direction of the paper machine. A transverse flow, which produces distortion of the fibre orientation, affects the quality factors of the paper produced, such as the dimensional stability of the paper in connection with changes in moisture. In particular, it is an important requirement that the main axes of the directional distribution, i.e. orientation, of the fibre mesh in the paper coincide with the directions of the main axes of the paper and that the orientation is symmetric in relation to these axes. At the edges of the pulp-flow duct in the headbox, of course, owing to the vertical walls, there is a higher friction. This edge effect produces a very strong linear distortion in the profile. Profile faults in the turbulence generator of the headbox usually produce a non-linear distortion in the profile inside the lateral areas of the flow ducts. Attempts are made to compensate for an unevenness of the grammage profile arising from the drying-shrinkage of paper by means of a crown formation of the slice, so that the slice is thicker in the middle of the pulp jet. When the paper web is dried, it shrinks in the middle area of the web to a lower extent than in the lateral areas, the shrinkage being, as a rule, in the middle about 1...3 % and in the lateral areas about 4...6 %. Said shrinkage profile produces a corresponding change in the transverse grammage profile of the web so that, owing to the shrinkage, the dry grammage profile of a web whose transverse grammage profile was uniform after the press is changed during the drying so that, in both of the lateral areas of the web, the grammage is slightly higher than in the middle area. As is known from the prior art, said grammage profile has been regulated by means of the profile bar so that the profile bar of the headbox is kept more open in the middle area than in the lateral areas. By means of said arrangement, the pulp suspension is forced to move towards the middle area of the web. Said circumstance further affects the alignment of the fibre orientation. The main axes of the directional distribution, i.e. orientation, of the fibre mesh should coincide with the directions of the main axes of the paper, and the orientation should be symmetric in relation to these axes. In said regulation of the profile bar, a change in the orientation is produced as the pulp suspension flow receives components in the transverse direction. Regulation of the lip of the headbox also produces a change in the transverse flows of the pulp jet even though the objective of the regulation is exclusively to affect the grammage profile, i.e. the thickness profile of the pulp suspension layer that is fed. Thus, the transverse flows have a direct relationship with the distribution of the fibre orientation. From the prior art, solutions of equipment are known separately by whose means attempts are made to regulate the fibre orientation, and solutions of equipment are known separately by whose means attempts are made to regulate the grammage profile of the web. However, when the grammage profile is regulated in a prior-art solution by means of the profile bar, the fibre orientation in the web is unavoidably also affected at the same time. From the prior art, a method is known in the headbox of the paper machine for the control of the distortion of the fibre orientation in the paper web. In the method, medium flows are passed into lateral passages placed at the level of the turbulence generator of the headbox, and, by regulating the magnitudes and the mutual proportions of said flows, the transverse flows of the pulp suspension are affected, and thereby the distortion of the fibre orientation is regulated. By means of the flows introduced into the lateral passages, a transverse flow velocity is produced which compensates for the distortion of the fibre orientation. On the other hand, from the applicant's Patent US-A-5 022 965 of earlier date, a method is known in the headbox of a paper machine for the control of the distribution of the fibre orientation of the paper web in the transverse direction of the machine, in which method the transverse velocity component of the discharge jet is regulated by aligning the turbulence tube of the turbulence generator. By means of the above prior-art methods for the control of the fibre orientation in the paper web, it is, as a rule, possible to control the linear distortion profiles only. The prior-art methods are suitable for the control of the fibre orientation, but, when they are used, commonly even a large non-linear residual fault remains in comparison with an even distribution of the orientation. The prior-art methods are well suitable for basic regulation of the distortion of the orientation. However, by means of the prior-art methods, it is not possible to regulate individual faults, which may occur in the orientation in the middle area of the web and which arise, e.g., from defects in the pipe system of the turbulence generator. A number of methods are also known for the regulation of the profile bar, in which cases, while the grammage profile is measured, the position of the profile bar in the headbox of the paper machine is changed and, by means of the profile bar, the thickness of the pulp suspension discharged onto the wire, and thereby, the grammage of the paper web are affected. In the way described above, said regulation, however, produces faults in the orientation, because, by means of the regulation, the flow is throttled elsewhere, whereby components of transverse velocity are produced in the flow. From the prior art, EP-A-462 472 is known, in which the headbox has been divided across its width into compartments by means of partition walls and in which solution, in an individual compartment, there is at least one inlet duct for the passage of a component flow. Moreover, in the solution, in front of the individual inlet duct, a mixer is connected by whose means the pulp suspension ratio can be regulated. The preamble of claims 1 and 6 is based on EP-A-462 472. DE-A-4 112 347 is also relevant prior art. In the present application, a solution of equipment is described, by whose means the consistency of the pulp suspension can be regulated without producing a change in the flow quantity. A solution is also described in which, by means of the device, it is also possible to regulate the pressure level of the overall flow departing from the mixer and, thus, the flow quantity and the flow velocity while the mixing ratio remains at its specified invariable value. In the solution of the present invention, the mixer comprises a distributor part, by whose means both the throttle, i.e. the flow resistance, of the inlet duct for the first component flow connected with the mixer and the throttle, i.e. the flow resistance, of the flow in the inlet duct for the second component flow connected with the mixer are regulated at the same time. By means of the device and the method in accordance with the invention, it is possible to control the grammage orientation profile of the paper web reliably across the web width, and also the fibre orientation profile of the paper web across the web width. In the solution in accordance with the invention, the grammage profile is affected by to the pulp flow adding a component flow whose concentration differs from the average concentration of the pulp flow. In the solution in accordance with the invention, two component flows are introduced into the mixer, and the mixing ratio is regulated continuously so that, when the throttle of the pulp flow or 0-water flow in one component-flow duct is increased, the throttle of the other component flow is reduced, or the other way round. Thus, in the regulation, the concentration of the overall pulp flow departing from the mixer is affected continuously and, yet, the quantity of said concentration is kept invariable. Thus, in the mixer, to the pulp flow, it is possible to add, for example, water alone, 0-water, or a diluted pulp suspension whose concentration and/or chemical composition differ(s) from the concentration of the main pulp flow. The pulp suspension that has been regulated in the mixer is passed into the main pulp flow. In the prior-art solution, the grammage profile was altered by acting upon the pressure in the discharge duct by means of the profile bar. In the solution of equipment in accordance with the invention, a profile bar is not needed necessarily, because the fibre orientation profile is regulated by means of local component flows passed into different positions of width across the headbox. In the solution in accordance with the invention, the headbox comprises separate blocks across the width of the headbox, into which blocks it is possible to feed an additional flow, whose consistency has been regulated to the desired level and by means of which additional flow a fault in the grammage profile occurring in a certain width position of the web is corrected. Thus, into a certain position of width of the headbox, it is possible to introduce a pulp suspension thicker than average or a pulp suspension more dilute than average, depending on the measured grammage profile error, so as to correct said profile error. However, it is essential in the regulation of the grammage profile that, during the regulation of the concentration, the flow quantity of the additional flow Q 3 is kept invariable and that, thus, during the regulation of the consistency, no changes are produced in the overall flow-velocity profile of the pulp suspension in the headbox. Thus, by means of the width-specific additional flows Q 3.1 ,Q 3.2 ...Q 3.n in the headbox, in the regulation of the consistency, the consistency of the pulp suspension is affected at a certain position of width only. Thus, by means of the additional flows Q 3.1 ,Q 3.2 ...Q 3.n , faults occurring in the grammage profile are corrected. Also, in the solution of equipment and method in accordance with the invention, it is possible to regulate the fibre orientation, the pressure profile, and thereby the velocity profile by regulating the flow quantities of the flows Q 3.1 , Q 3.2 ...Q 3.n while the mixing ratio remains at its regulated value. Thus, when the fibre orientation profile is supposed to be corrected, the flow velocity profile coming out of the pipe system of the turbulence generator is affected locally in the direction of width of the web by means of regulation of the flow quantities of the flows Q 3.1 ,Q 3.2 ...Q 3.n . In this way, at a certain position of width of the web, locally the pressure level and thereby the flow velocity and further the flow quantity are increased, or, if necessary, reduced. In this way it is possible to act upon local profile faults occurring in the fibre orientation. The method in accordance with the invention of regulating a headbox is characterized by the features of the characterizing clause of claim 1. The headbox in accordance with the invention is characterized by the features of the characterizing clause of claim 6. The invention will be described in the following with reference to some preferred embodiments of the invention illustrated in the figures in the accompanying drawings, the invention being, however, not supposed to be confined to said embodiments alone. Figure 1 illustrates the development of different profiles when proceeding in the machine direction of the paper machine from the turbulence generator. Figure 2A is a sectional view of a headbox of a paper machine in accordance with the present patent application. Figure 2B is an illustration in the direction K 10 in Fig. 2A. Figure 3 is a partial illustration of principle of a mixer unit, by whose means a fault in the grammage profile and a fault in the fibre orientation profile can be corrected locally in the direction of width of the web. Figure 4A is an illustration of principle of a first position of regulation. Figure 4B shows a second position of regulation. Figure 4C shows a third position of regulation. Figure 5A shows an embodiment of a mixer unit in accordance with the invention which corresponds to the illustrations of principle in Fig. 3 and in Figs. 4A...4C. Fig. 5A is a sectional view of the mixer unit in accordance with the invention. Figure 5B is an illustration in the direction K 1 indicated in Fig. 5A. Figure 5C is an illustration in the direction K 2 indicated in Fig. 5A. Figure 5D is an illustration in the direction K 3 indicated in Fig. 5A. Figure 5E is an axonometric view of the distributor part of the mixer unit. Figure 6A is a sectional view of an embodiment of a mixer unit, wherein the flow into the inlet chamber of the mixer unit is distributed by means of a separate tumbler piece, which is placed in different closing positions in relation to the inlet openings, in which case, when one inlet opening is being opened, the other inlet opening is closed by the corresponding amount. Figure 6B is a sectional view taken along the line I-I in Fig. 6A. Figure 7A shows an embodiment of the invention corresponding to Fig. 6A,6B, except that in the embodiment of Figs. 7A,7B the flow quantity of the departing flow Q 3 can also be regulated. Fig. 7A is a sectional view of the mixer unit 22. Figure 7B is a sectional view taken along the line II-II in Fig. 7A. By means of Fig. 1, the development of different profiles is illustrated when proceeding in the machine direction of the paper machine from the turbulence generator to the forming wire and forwards. In the description related to Fig. 1, reference is made to the different positions illustrated in the figure when moving forwards from the turbulence generator in the direction of flow of the pulp suspension in the paper machine. Section A-A: At the beginning of the slice cone, the flow state after the turbulence generator (TG) consists of the pressure and thickness profiles. In the embodiments that are used commonly, attempts are made to make these profiles as straight as possible. If the pressure profile of the feed from the TG is not uniform, the velocity profile in the machine direction (KS) tends to be equalized during the acceleration in the slice cone and produces transverse flow components. The transverse flows are retained up to the free jet and produce a directional-angle profile in the jet. Section B-B: In the applications that are used commonly, the fibre grammage profile is regulated by profiling the thickness profile of a pulp of uniform consistency, e.g., by means of the profile bar. This, however, produces transverse volumetric flows, which are also seen in the directional profile of the jet, which may partly also arise from the pressure profile of the section A-A. Section C-C: The fibre suspension is filtered on the wire part, after which the individual fibres have been bound into the structure of the paper. The fibres are oriented in accordance with the difference between the direction and velocity of the jet coming from the headbox and velocity and running direction of the wire (filtered material). In local filtering, there may be differences arising from local variations in retention. Section D-D: Depending on the moisture profile and on differences in the transverse holding forces, the paper web shrinks unevenly during drying. In an area that shrinks extensively, the fibres and the fillers in the paper move closer to each other, whereby the grammage in the area increases and produces a need to lower the grammage. Thus, besides upon the grammage profile of the fibres, regulation of the grammage profile by means of the profile bar also acts upon the directional profile of the jet. Regulation of the thickness profile of the jet could be omitted entirely if the consistency profile after the TG could be regulated independently. In such a case, the jet is run as consistency-profiled and as of uniform thickness into the former. Further, when the pressure profile of the TG can be regulated, the directional-angle profile of the jet can be fine-adjusted separately. Fig. 2A shows a headbox as per the invention in connection with a twin-wire former. Of the former, Fig. 2A shows the breast rolls 10 and 11 and the forming wires 12 and 13 running over them, said forming wires defining the forming gap G between them. Out of the discharge duct 14 of the headbox, the pulp suspension jet is fed through the slice 15 into the forming gap G defined by the wires 12 and 13. Proceeding in the flow direction E of the pulp suspension, the headbox comprises an inlet header 16, a distributor manifold 17, an equalizing chamber 18, a turbulence generator 19, and a discharge duct 14. The discharge duct 14 is defined by a stationary lower-lip wall 20 and by an upper-lip wall 21 pivoting around a horizontal articulated joint M. As is shown in Fig. 2A, the solution of equipment comprises a mixer unit 22, into which a component flow Q 1 is introduced from the inlet header 100. Also, a second component flow Q 2 is introduced into the mixer unit 22, which flow is, in the embodiment shown in the figure, the pulp flow coming out of the inlet header 16. The flow Q 1 is preferably a diluting flow, whose concentration is, on the whole, different from the average concentration of the pulp suspension. The flow Q 1 consists preferably of diluting water. The combined flow Q 3 is passed through the throttle point 101 into the distributor pipe 28a and further, out of the distributor pipe, through the throttle point 102, into the turbulence tube 19a 1 of the turbulence generator 19 and further into the discharge duct 14. Fig. 2B is a top view of the solution of equipment shown in Fig. 2A, being a partial illustration of principle. As is shown in the figure, there are several mixer units 22a 1 ,22a 2 ...22a n placed side by side, and a diluting flow Q 1.1 ,Q 1.2 ...Q 1.n passes into said units out of the inlet header 100. In a corresponding way, into each mixer unit 22a 1 ,22a 2 ...22a n , a pulp suspension flow Q 2.1 ,Q 2.2 ...Q 2.n is passed out of the inlet header 16, said flows Q 1 and Q 2 being mixed together in each mixer unit 22a 1 ,22a 2 ... and being thereupon passed into the discharge duct 14. Thus, by means of each mixer unit 22a 1 ,22a 2 ...22a n , specifically in respect of each position of width of the headbox, it is possible to regulate the grammage and the fibre orientation of the web at the particular position of width by means of a flow Q 3.1 ,Q 3.2 ...Q 3.n passed into the pulp suspension. Said regulations are independent from one another. Fig. 3 shows a mixer unit 22 in accordance with the invention, by whose means it is possible to supply a pulp flow of desired consistency to a certain position of width of the headbox of the paper machine. By means of the mixer unit shown in Fig. 3, it is possible to regulate the grammage profile. In a corresponding way, by means of the mixer unit, it is possible to regulate the fibre orientation profile by acting upon the pressure loss in the pulp flow passing through the mixer unit and, thus, upon the velocity of the flow and further upon the flow quantity. As is shown in the illustration of principle in Fig. 3, the mixer unit 22 comprises a first inlet duct 23, through which the component flow Q 1 , preferably a so-called 0-water flow, is introduced into the chamber F of the mixer unit. Further, the mixer unit 22 comprises a second duct 24, through which the second component flow Q 2 , which is preferably a component flow at the average concentration of the pulp suspension, is introduced into the chamber F of the mixer unit 22. The flows pass, at the consistency ratio distributed by the distributor part 26, through the transverse duct 27 of the distributor part 26, placed in the chamber F, into the outlet duct 25. The combined flow Q 3 = Q 1 + Q 2 is passed to a certain position along the width of the headbox of the paper machine. According to the invention, each position of width of the paper machine comprises a separate duct 27a 1 , 27a 2 ..., in front of which there is a mixer unit 22a 1 ,22a 2 ,22a 3 ..., by whose means it is possible to regulate the concentration of the pulp suspension departing from the mixer units, and favourably also the flow velocity of said pulp suspension and, thus, the flow quantity. In the way shown in Fig. 3, the distributor part 26 can be displaced along a linear path (arrow L 1 ) in the chamber F, and said distributor part 26 can also be rotated (arrow L 2 ) in the chamber F. In such a case, the mouth part 27a of the flow duct 27 extending across the distributor part 26 can be brought into different positions in relation to the end openings 23a,24a of the inlet ducts 23 and 24. Thus, the flows Q 1 ,Q 2 in the ducts 23 and 24 can be regulated by increasing the throttle, i.e. the flow resistance, of the flow Q 1 in the duct 23 and reducing the throttle, i.e. the flow resistance, of the flow Q 2 in the duct 24, or the other way round. By shifting the distributor part 26 along a linear path, the mixing ratio of the flow Q 3 is affected, and rotation of the distributor part 26 affects the pressure loss in the flow Q 3 . Fig. 4A is an illustration of principle of a regulation in accordance with the invention. In the regulation position of Fig. 4A, the flow has access through the sectional flow areas U 1 and U 2 denoted by the shading into the duct 27 in the distributor part 26. The end opening of the duct 23 is denoted with 23a, and the end opening of the duct 24 is denoted with 24a. The sectional flow area of the end opening 23a is A 1 , and it corresponds to the sectional flow area of the end opening 24a. The shapes of the openings 23a and 24a are similar to one another. The central axis of the opening 23a is denoted with X 1 , and the central axis of the opening 24a is denoted with X 2 . The connecting line of the axes X 1 and X 2 is denoted with Y. The orifice of the flow duct 27 in the regulation part 26 is denoted with 27a in the figure. When the overall flow quantity Q 3 is increased, at the same time, the sectional flow area U 1 ,U 2 is increased through which the flow takes place into the duct 27 in the regulation part 26 and (in the way shown in the figure) the distributor part 26 is raised or lowered perpendicularly to the line Y (in the direction N). In a corresponding way, when exclusively the mixing ratio of the flows Q 1 ,Q 2 is supposed to be changed, the orifice 27a is displaced in the direction N', which is perpendicular to the direction N. The flow openings 23a,24a are arranged in such a way in relation to one another that at least one of the central planes coincide and that at least one central planes perpendicular to said central planes are parallel to one another. In Figs. 4A...4C, a solution as shown in the embodiment of Fig. 3 is examined, wherein the distributor part includes a duct 27, but it is obvious that the above examination also applies to the solution of the embodiment shown in Fig. 7, in which the distributor part 260 is a tumbler part, which does not include a separate transverse duct and by means of which tumbler part the end openings 23a,24a of the ducts 23,24 for the component flows are closed and opened. When the distributor part 26 is shifted along a linear path in the way shown in Fig. 4B, the sectional flow area U 1 of the component flow Q 1 coming from the duct 23 is increased, and the sectional flow area U 2 of the component flow Q 2 is reduced in the corresponding proportion. Thus, in the regulation, the mixing ratio is changed, but the sum of the flow quantities Q 3 = Q 1 + Q 2 remains invariable. If it is desirable to act upon the flow quantities of the flows Q 3.1 ,Q 3.2 ...Q 3.n in the way shown in Fig. 4C, the distributor part 26 is shifted to the side (arrow L 2 ), in which case, at the same time, the sectional flow areas U 1 and U 2 are reduced. When the sectional flow areas U 1 ,U 2 are increased, the mixing ratio must remain unchanged. If U 1 was, in the initial situation, larger than U 2 , U 1 is increased by a larger amount than U 2 . In a corresponding way, when the sectional flow areas U 1 and U 2 are reduced, and if U 1 is larger than U 2 , the reduction of U 1 must be greater than the reduction of U 2 . The valve solution in accordance with the invention achieves the keeping of the mixing ratio invariable in the regulation of the flow quantity. Thus, in said regulation of the flow quantity, when the distributor part 26 is rotated, the pressure loss of the flow is affected, and thereby the velocity profile of the flow and further the fibre orientation profile are affected. The regulation does not affect the concentration of the flow Q 3 , and thereby the concentration D 3 of the pulp suspension in the overall flow Q 3 flowing out of the duct 25 is kept at its desired regulated value. Fig. 5A is a sectional view of a first preferred embodiment of a mixer unit in accordance with the invention, which corresponds to the illustrations in Figs. 3 and 4A...4C. As was described above, the mixer unit 22 comprises a first inlet duct 23 and a second inlet duct 24 as well as an exhaust duct 25. The mixer unit comprises a chamber F, in which the distributor part 26 is fitted to be displaceable along a linear path (arrow L 1 ) and in which it is fitted to be rotatable (arrow L 2 ). When the distributor part 26 is displaced along a linear path perpendicularly to the inlet axes X 1 ,X 2 and X 3 of the ducts 23,24,25 (arrow L 1 ), the position of the inlet opening 27a of the transverse duct 27 in the distributor part 26 in relation to the end opening 23a of the first inlet duct 23 and to the end opening 24a of the second inlet duct 24 is affected. Thus, when the distributor part 26 is raised or lowered (arrow L 1 ), the flow is increased through the first inlet duct 23 into the transverse duct 27 in the distributor part 26, and the flow through the second inlet duct 24 is reduced by the corresponding amount, or the other way round. Thus, the mixing ratio between the component flow Q 1 coming from the inlet duct 23 and the component flow Q 2 coming from the other inlet duct 24 is changed, but the overall flow quantity Q 3 = Q 1 + Q 2 of said component flows Q 1 ,Q 2 is kept invariable. Out of the first inlet duct 23, preferably 0-water is made to flow. Out of said flow duct 23, it is also possible to pass a pulp suspension whose concentration is, on the whole, different from the average concentration of the pulp suspension in the headbox, the pulp of average concentration being made to flow preferably through the second inlet duct 24. When the distributor part 26 is rotated (arrow L 2 ), at the same time the throttle of the flow Q 1 coming out of the first inlet duct 23 and the throttle of the flow Q 2 coming out of the second inlet duct 24 are affected so that the flow resistances of said flows out of the ducts 23 and 24 are increased or reduced at the same time. Thus, by rotating the distributor part 26, the pressure loss of the combined flow Q 3 = Q 1 + Q 2 is affected. When the pressure loss is increased or reduced, the flow quantity of the flow Q 3 through the outlet duct 25 is increased or reduced. In this way it is possible to affect the velocity profile of the flow and further the pulp fibre orientation profile at the desired position along the width of the paper machine in the desired way. Fig. 5B is an illustration in the direction K 1 indicated in Fig. 5A. Fig. 5C is an illustration in the direction K 2 indicated in Fig. 5A. Fig. 5D is an illustration in the direction K 3 in Fig. 5A, i.e. from above. Fig. 5E is an axonometric illustration of a disassembled distributor part 26 of the mixer unit 22 in accordance with the invention. Fig. 6A is a sectional view of an embodiment of a mixer unit 22 falling outside the scope of the claims. Also in this embodiment, the mixer unit 22 comprises a first inlet duct 23 and a second inlet duct 24 and an outlet duct 25, through which the combined flow Q 3 = Q 1 + Q 2 is removed. The distributor part 260 comprises a displacing spindle 260a, by whose means the distributor part 260 can be shifted into different covering positions in relation to the end opening 23a of the first inlet duct 23 and in relation to the end opening 24a of the second inlet duct 24. Through the first inlet duct 23, preferably 0-water is introduced. It is also possible to make such a pulp suspension flow through the duct 23 whose concentration is, on the whole, different from the average concentration of the pulp suspension in the headbox, said pulp suspension of average concentration being made to flow preferably through the second inlet duct 24. Thus, in the way shown in Fig. 6A, when the spindle 260a is rotated (arrow L 3 ), the distributor part 260, which operates as a tumbler part, is shifted into different covering positions in relation to the end openings 23a,24a. When the distributor part 260 is displaced, the end opening 23a of the inlet duct 23 is opened, and the end opening 24b of the inlet duct 24 is closed by the corresponding amount, or the other way round. Thus, also in this embodiment of equipment, the mixing ratio can be regulated continuously and, yet, the flow quantity of the combined flow Q 3 remains invariable, i.e. the pressure loss remains at its invariable value. The duct 25 is passed to the desired position of width of the headbox of the paper machine. Thus, in the direction of width, the headbox of the paper machine comprises a number of ducts 25a 1 ,25a 2 ..., which are opened preferably into separate distribution pipes 28a 1 ,28a 2 , each of which passes directly into a turbulence tube 19a 1 ,19a 2 ... of its own placed in the same position of width in the turbulence generator 19. Fig. 6B is a sectional view taken along the line II-II in Fig. 6A. The spindle 260a is rotated by means of the lever 260b. Fig. 7A shows an embodiment of the invention which is in the other respects similar to the embodiment of Figs. 6A and 6B, but in the solution of said embodiment, the flow quantity of the departing flow can also be regulated so that the mixing ratio remains at its regulated invariable value. In the solution of Fig. 7A, the spindle 260a is displaced along a linear path in the way indicated by the arrow L 5 , in which case the distributor part 260 connected with the spindle is placed in different covering positions in relation to the end openings 23a,24a so that, at the same time, the end openings 23a,24a are closed or opened. The regulation of the mixing ratio takes place so that the spindle 260 is rotated (arrow L 4 ), whereby the distributor part 260 is shifted into different covering positions in relation to the end openings 23a,24a, and so that, when the sectional flow area of one end opening is increased, the sectional flow area of the other opening is reduced by the corresponding amount, and the other way round. Fig. 7B is a sectional view taken along the line II-II in Fig. 7A. In the way indicated in Fig. 7B by means of the arrow L 5 , the distributor part 260 can be shifted along a linear path, whereby, at the same time, the end openings of the ducts 23 and 24 are opened or closed, in which case the throttle of the outlet flow Q 3 is reduced or increased while the mixing ratio of the flows Q 1 and Q 2 remains at its invariable value.

Claims: Method of regulating a headbox by introducing an additional flow (Q 3 ) into the pulp suspension at different points across the width of the headbox, the additional flow (Q 3 ) being provided as the outlet flow from a mixer unit (22) in which two component flows (Q 1 , Q 2 ) of different concentrations are introduced, in which method the concentration of the additional flow (Q 3 ) can be regulated by adjusting the mixing ratio of the two component flows (Q 1 , Q 2 ) without affecting the flow rate of the additional flow (Q 3 ) and the flow rate of the additional flow (Q 3 ) can be regulated without affecting the mixing ratio of the two component flows (Q 1 , Q 2 ), characterized in that the two component flows (Q 1 , Q 2 ) are introduced in a chamber (F) of the mixer unit (22), the concentration and flow rate of the additional flow (Q 3 ) are regulated by means of a distributor part (26, 260) of the mixer unit (22) which is displaceable in said chamber (F), the concentration of the additional flow (Q 3 ) is regulated by displacing the distributor part (26, 260) such that the flow resistance of one of said two component flows (Q 1 , Q 2 ) entering into the chamber (F) is increased and the flow resistance of the other one of said two component flows (Q 1 , Q 2 ) entering into the chamber (F) is reduced by the corresponding amount, whereby the mixing ratio of the two component flows (Q 1 , Q 2 ) is adjusted without affecting the flow rate of the additional flow (Q 3 ), and the flow rate of the additional flow (Q 3 ) is regulated by displacing the distributor part (26, 260) such that the flow resistances of the two component flows (Q 1 , Q 2 ) entering into the chamber (F) are increased or reduced simultaneously at a specific mixing ratio. Method as claimed in claim 1, characterized in that the concentration and flow rate of the additional flow (Q 3 ) are regulated by shifting the distributor part (26, 260) along a linear path or rotating the distributor part (26, 260) by means of a spindle (26a, 260a) connected to the distributor part (26, 260). Method as claimed in any of the preceding claims, characterized in that the two component flows (Q 1 , Q 2 ) are directed into said chamber (F) by means of two inlet ducts (23, 24), and that the distributor part (26) used comprises a duct (27) which can be placed into different positions in relation to the end openings (23a, 24a) of the two inlet ducts (23, 24) into said chamber (F). Method as claimed in claim 3, characterized in that the distributor part (26) can be placed into different covering positions to close and open said end openings (23a, 24a). Method as claimed in claim 1 or 2, characterized in that the two component flows (Q 1 , Q 2 ) are directed into said chamber (F) by means of two inlet ducts (23, 24), that the flow rate of the additional flow (Q 3 ) is regulated by displacing the distributor part (260) along a linear path in a direction (L 5 ) perpendicular to the line connecting the central axes of the end openings (23a, 24a) of the two inlet ducts (23, 24) into the chamber (F), and that the concentration of the additional flow (Q 3 ) is regulated by rotating the distributor part (260) about an axis parallel to the direction (L 5 ) of said linear path. Headbox which is regulated by introducing an additional flow (Q 3 ) into the pulp suspension at different points across the width of the headbox, the headbox comprising a device by means of which the concentration of said additional flow (Q 3 ) can be adjusted without affecting the flow rate thereof and the flow rate of the additional flow (Q 3 ) can be adjusted without affecting the concentration thereof, wherein the device comprises a mixer unit (22), an outlet duct (25) for the additional flow (Q 3 ) and two inlets ducts (23, 24) through which two component flows (Q 1 , Q 2 ) of different concentrations are passed into the mixer unit (22), characterized in that the mixer unit (22) comprises a chamber (F) into which the two component flows (Q 1 , Q 2 ) are passed by means of said inlet ducts (23, 24), the mixer unit (22) further comprises a distributor part (26, 260) which is displaceable in said chamber (F), which distributor part (26, 260) can be brought into different covering positions in relation to the end openings (23a, 24a) of the inlet ducts (23, 24) into the chamber (F) to close or open said end openings (23a, 24a), the distributor part (26, 260) is such that it can be displaced so that the throttle of one of the two component flows (Q 1 , Q 2 ) is increased and the throttle of the other one of the two component flows (Q 1 , Q 2 ) is reduced by the corresponding amount whereby the concentration of the additional flow (Q 3 ) can be adjusted without affecting the flow rate thereof, and the distributor part (26, 260) is such that it can be displaced so that the throttles of the component flows (Q 1 , Q 2 ) are increased or reduced simultaneously, whereby the flow rate of the additional flow (Q 3 ) can be adjusted without affecting the mixing ratio of the two component flows (Q 1 , Q 2 ). Headbox as claimed in claim 6, characterized in that the distributor part (26) is connected to a shifting spindle (26a), by whose means the distributor part (26) can be displaced. Headbox as claimed in claim 6 or 7, characterized in that the distributor part (26) comprises a duct (27) having an opening (27a) which can be brought into different positions in relation to said end openings (23a, 24a), that the concentration of the additional flow (Q 3 ) can be adjusted by displacing the distributor part (26) along a linear path, and that the flow rate of the additional flow (Q 3 ) can be adjusted by rotating the distributor part (26). Headbox as claimed in claim 6, characterized in that the distributor part (260) is a displaceable tumbler part, which can be brought into different covering positions in relation to said end openings (23a, 24a). Headbox as claimed in claim 9, characterized in that the distributor part (260) is connected to a rotatable spindle (260a) which can also be displaced linearly in a direction (L 5 ) parallel to its axis of rotation, whereby by rotating of said spindle (260a) the distributor part (260) can be brought into different covering positions in relation to said end openings (23a, 24a) to regulate the concentration of the additional flow (Q 3 ) by adjusting the throttles of the component flows (Q 1 , Q 2 ) relative to one another without affecting the flow rate of the additional flow (Q 3 ), and whereby by displacing said spindle (260a) linearly the distributor part (260) can brought into different covering positions in relation to said end openings (23a, 24a) to regulate the flow rate of said additional flow (Q 3 ) by increasing or reducing the throttles of the component flows (Q 1 , Q 2 ) simultaneously without affecting the concentration of the additional flow (Q 3 ).

Inventors: HUOVILA JYRKI, NYBERG PETRI, VIITANEN OLAVI, HUOVILA, JYRKI, NYBERG, PETRI, VIITANEN, OLAVI
Applicants: VALMET CORP, VALMET CORPORATION
Application year: 1994
Main classification: D21F1
IPC codes: D21F1